netdev - Re: [PATCH net-next v2 2/4] Documentation: net: phy: Add a paragraph about pause frames/flow control

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Message-ID: <1b7425f7-9183-69d4-76e8-42eefffeb1c6@laposte.net>
Date:   Mon, 28 Nov 2016 11:38:19 +0100
From:   Sebastian Frias <sf84@...oste.net>
To:     Florian Fainelli <f.fainelli@...il.com>, netdev@...r.kernel.org
Cc:     davem@...emloft.net, andrew@...n.ch,
        martin.blumenstingl@...glemail.com, mans@...sr.com,
        alexandre.torgue@...com, peppe.cavallaro@...com,
        timur@...eaurora.org, jbrunet@...libre.com
Subject: Re: [PATCH net-next v2 2/4] Documentation: net: phy: Add a paragraph
 about pause frames/flow control

On 27/11/16 19:44, Florian Fainelli wrote:
> Describe that the Ethernet MAC controller is ultimately responsible for
> dealing with proper pause frames/flow control advertisement and
> enabling, and that it is therefore allowed to have it change
> phydev->supported/advertising with SUPPORTED_Pause and
> SUPPORTED_AsymPause.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  Documentation/networking/phy.txt | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/networking/phy.txt b/Documentation/networking/phy.txt
> index 4b25c0f24201..9a42a9414cea 100644
> --- a/Documentation/networking/phy.txt
> +++ b/Documentation/networking/phy.txt
> @@ -127,8 +127,9 @@ Letting the PHY Abstraction Layer do Everything
>   values pruned from them which don't make sense for your controller (a 10/100
>   controller may be connected to a gigabit capable PHY, so you would need to
>   mask off SUPPORTED_1000baseT*).  See include/linux/ethtool.h for definitions
> - for these bitfields. Note that you should not SET any bits, or the PHY may
> - get put into an unsupported state.
> + for these bitfields. Note that you should not SET any bits, except the
> + SUPPORTED_Pause and SUPPORTED_AsymPause bits (see below), or the PHY may get
> + put into an unsupported state.
>  
>   Lastly, once the controller is ready to handle network traffic, you call
>   phy_start(phydev).  This tells the PAL that you are ready, and configures the
> @@ -139,6 +140,19 @@ Letting the PHY Abstraction Layer do Everything
>   When you want to disconnect from the network (even if just briefly), you call
>   phy_stop(phydev).
>  
> +Pause frames / flow control
> +
> + The PHY does not participate directly in flow control/pause frames except by
> + making sure that the SUPPORTED_Pause and SUPPORTED_AsymPause bits are set in
> + MII_ADVERTISE to indicate towards the link partner that the Ethernet MAC
> + controller supports such a thing. Since flow control/pause frames generation
> + involves the Ethernet MAC driver, it is recommended that this driver takes care
> + of properly indicating advertisement and support for such features by setting
> + the SUPPORTED_Pause and SUPPORTED_AsymPause bits accordingly. This can be done
> + either before or after phy_connect() 

If the bits are set after phy_connect(), how does the PHY framework knows there's
an update to the bits? Should some call be made?

and/or as a result of implementing the
> + ethtool::set_pauseparam feature.
> +
> +
>  Keeping Close Tabs on the PAL
>  
>   It is possible that the PAL's built-in state machine needs a little help to
>